I think my 2006 Subaru Forester rear differential is going bad. on 2006 Subaru Forester

It has started to buck and jerk while driving and now has started to actaully fill like it is not grabbing at all at times.Is this dangreous and what could happen? And what are the average costs for this kind of repair? And should i go to a dealer or a mechanic who has a good reputation with Subaru?

Asked by for the 2006 Subaru Forester
diff needs to be insp to determine cost